The present invention relates to array antennas and particularly to antennas designed to radiate within a limited angular region of space.
In their U.S. Pat. No. 4,041,501 Frazita, et al. describe a limited scan array antenna system with a sharp cut-off of the element pattern. In accordance with the Frazita disclosure there is provided a coupling network for interconnecting the input terminals of a plurality of antenna element modules and the corresponding antenna elements of each module. In addition, the network interconnects the element modules so that signals supplied to any of the input terminals are supplied primarily to the elements of the corresponding element module, and also supplied to selected elements in other element modules of the array. As a result of this selective coupling, the antenna aperture can be provided with an aperture excitation corresponding approximately to a sine x/x element distribution for input signals supplied to any of the input terminals of the coupling network. Accordingly, supplying wave energy signals to any one of the input terminals causes the antenna array to radiate an effective pattern which corresponds to the radiation pattern approximately radiated by a sine x/x aperture distribution, that is, an element pattern with a substantially uniform amplitude over a selected angular region of space, and effectively no radiation over remaining regions of space in which it is desired to suppress radiation. The effective element spacing of the array can be increased to the point where grating lobes, which might occur during the scanning of a radiation beam through the desired region of space are allowed to occur in regions of the antenna element pattern wherein antenna radiation is suppressed. As a result, a substantially larger effective element spacing can be used for a limited scan array antenna, and the number of active elements, for example, phase shifters, needed for the operation of the array antenna in a particular system, such as a microwave landing system, can be substantially reduced.
Another antenna system having a modular coupling network for effecting a similar control of element radiation pattern has been described in the pending application of Harold Wheeler, U.S. Pat. No. 4,143,379 issued Mar. 6, 1979. While both of these prior art systems, and particularly the Frazita et al. patent, describe systems which are capable of providing effective control of an antenna element pattern in order to achieve an element pattern which permits a larger effective element spacing with a consequent savings in antenna control components for a limited scan antenna; these prior art systems are most useful over only a limited frequency band, as is the case for the apparatus described in the Frazita patent, or may involve a complex network of interconnections, as in the apparatus described in the Wheeler patent.
It is an object of the present invention to provide an array antenna system having control of antenna element pattern in order to effectuate the element pattern control and cost savings of the aforementioned patent and application, wherein there is provided a simplified coupling network, which is operable over a relatively large frequency band.